Since print systems have been in existence, printers have sought methods for inhibiting counterfeiting and unauthorized copying of printed documents. Enhanced complexity in an engraved pattern of a press plate is one such method that most people are familiar with as a result of its everyday observation in currency bills. Bank checks, security documents, bonds and other financial documents are other examples of printed documents having complex background patterns to inhibit unauthorized reproduction. Identification documents, e.g. passports, social security cards and the like, are other examples. Credit cards not only have complex background patterns, but now also have embedded holographics to enhance verification and authentication of such a card.
As far as printed documents are concerned, a common complex background pattern is a guilloché line pattern, i.e., an ornamental pattern or border consisting of lines flowing in interlaced curves. FIG. 5 is a check pattern exemplifying a guilloché. The guilloché patterns are designed to be hard to reproduce and thus can serve as a security feature. However, an associated disadvantage is that the applied pattern or information is often fixed in nature. Accordingly, the fixed nature of the pattern means that it is common and identical on all documents on which it is printed. Often it is preprinted on the document before the document is usually used (e.g., checks).
More particularly, even though such background patterns are designed to be hard to reproduce, at the same time, they are fixed, meaning every passport has the same pattern as all passports from that country, every monetary note has the same pattern as the same note from that country, any credit card has the same pattern, etc. This actually decreases the amount of security afforded by a guilloché since it is sufficient to re-create one pattern in order to counterfeit N credit cards. It would therefore be desirable and a substantial improvement to have a variable guilloché, where, for example, the credit card number is embedded in the guilloché and thus every credit card has a different pattern (to a decoder) while having the identical human visual impression.
There is a need for embedding security information that more particularly identifies a particular document in a unique manner so that whatever information is embedded is visually imperceptible to an intended counterfeiter or unauthorized copyist even for a single document produced in a print run of the one document only.
Glyph technology, cf. U.S. Pat. No. 5,449,896, is another well known security system which can uniquely identify a document, but the inclusion of a glyph code (or any bar coding system of that type) is easily humanly perceptible for its inclusion on the document, although the meaning of the glyph itself is generally only machine decodable.
There also exist various digital watermarking methods that embed information into images. However, most such methods were designed mainly for continuous-tone pictorial type images. They often modulate the intensity (color) of individual pixels. When applied to line patterns, these methods result in isolated pixels that cannot be reliably printed.
One common aspect of all such security feature applications is the addition of some kind of information into the document that prevents/hinders alterations and counterfeiting.
There is thus a need for a system which better hides security data within a printed document, and that which can embed security data unique to that particular document so that the security information is successfully implemented for even a document production run of one document.